A new structure of spiral groove dry gas seal was designed with two combined spiral grooves.The combined spiral grooves consist of large spiral grooves processed along the outside edge of the seal and small spiral grooves along the roots of the large ones.The performance of this seal was simulated by Fluent and the results were compared with a common spiral groove dry gas seal.The structure parameters of seal end face were optimized with the objective functions of opening force,leakage and torque by orthogonal method.The results show that the combined spiral groove dry gas seal has better performance than the common one with same structure parameters,which has more obvious advantages of reducing leakage at higher pressure,deeper groove and higher ratio of groove width and ridge width of spiral groove.The optimal structure parameters corresponding to opening force,leakage and torque are different for the combined spiral groove dry gas seal,hence it is necessary to choose an appropriate combination of seal end face structure parameters to meet the demand in the design of dry gas seals.